The present application is based on Japanese Patent Application No. 2001-192573 and Japanese Patent Application No. 2001-290329 filed in Japan, the contents of which are fully incorporated herein.
1. Field of the Invention
The present invention relates to a method of, and apparatus for, manufacturing a field emission-type electron source comprising a strong field drift layer so as to emit an electron beam by electric field emission.
2. Description of the Related Art
There is well known a field emission-type electron source (hereinafter, simply referred to as an xe2x80x9celectron sourcexe2x80x9d) in which a strong field drift layer (hereinafter, simply referred to as a xe2x80x9cdrift layerxe2x80x9d) consisting of a porous semiconductor layer oxide (or nitride) is formed on one surface of an electrically conductive substrate, and a surface electrode is formed on the drift layer (for example, refer to Japanese Patent Application Publication No. 2966842, Japanese Patent Application Publication No. 2987140, and Japanese Patent Application Publication No. 3079086). As an electrically conductive substrate, for example, there are employed: a semiconductor substrate whose resistivity is comparatively close to conductivity of a conductor; a metal substrate; and a substrate having an electrically conductive layer formed on one surface of a glass substrate (insulating substrate) or the like.
For example, as shown in FIG. 26, in an electron source 10xe2x80x2 of this type, a drift layer 6xe2x80x2 consisting of an oxidized porous polycrystalline silicon layer is formed on a main surface of an n-type silicon substrate 1 that is an electrically conductive substrate. A surface electrode 7 is formed on the drift layer 6xe2x80x2. An ohmic electrode 2 is formed on a back face of the n-type silicon substrate 1. In an example shown in FIG. 26, a semiconductor layer 3 consisting of a non-doped polycrystalline silicon layer is interposed between the n-type silicon substrate 1 and the drift layer 6xe2x80x2. However, there is proposed an electron source having the drift layer 6xe2x80x2 formed on the main surface of the n-type silicon substrate 1 without interposing the semiconductor layer 3.
In the electron source 10xe2x80x2 shown in FIG. 26, electrons are emitted in accordance with the following process. First, a collector electrode 21 is disposed in opposite to the surface electrode 7. While vacuuming is provided between the surface electrode 7 and the collector electrode 21, a direct current voltage Vps is applied between the surface electrode 7 and the n-type silicon substrate 1 so that the surface electrode 7 becomes high in potential (positive polarity) relevant to the n-type silicon substrate 1 (ohmic electrode 2). On the other hand, a direct current voltage Vc is applied between the collector electrode 21 and the surface electrode 7 so that the collector electrode 21 becomes high in potential relevant to the surface electrode 7. When the direct current voltages Vps and Vc are properly set, electrons injected from the n-type silicon substrate 1 drift the drift layer 6xe2x80x2, and is emitted trough the surface electrode 7 (the singly dotted chain line in FIG. 26 indicates the flow of an electron xe2x80x9cexe2x80x9d emitted through the surface electrode 7). The surface electrode 7 is formed of a material with its small work function (for example, gold). The thickness of the surface electrode 7 is set to about 10 nm to 15 nm.
Here, a current flowing between the surface electrode 7 and the ohmic electrode 2 is referred to as a diode current Ips, and a current flowing between the collector electrode 21 and the surface electrode 7 is referred to as an emission current (emission electron current) Ie. At this time, as a rate (=Ie/Ips) of the emission current Ie relevant to the diode current Ips increases, the electron emission efficiency is high.
In the electron source 10xe2x80x2, even if the direct current voltage Vps applied between the surface electrode 7 and the ohmic electrode 2 is defined as a low voltage of about 10V to 20V, electrons can be emitted. In addition, in the electron source 10xe2x80x2, the dependency in degree of vacuum in electron emission characteristics can be reduced, and electrons can be emitted constantly with high emission efficiency without generating a hopping phenomenon during electron emission.
In a process for manufacturing the electron source 10xe2x80x2, the step of forming the drift layer 6xe2x80x2 includes the film forming step, anodic oxidation processing step, and oxidizing step. In the film forming step, a non-doped polycrystalline silicon layer is deposited on one surface of the n-type silicon substrate 1 that is an electrically conductive substrate. In the anodic oxidation processing step, the polycrystalline silicon layer is anodically oxidized, whereby a porous polycrystalline silicon layer containing polycrystalline silicon grains and silicon nanocrystals is formed. In the oxidizing step, the porous polycrystalline silicon layer is oxidized in accordance with a rapid thermal oxidization technique, and thin oxide films are formed respectively on the surfaces of the grain and silicon nanocrystals. In the anodic oxidation processing step, a mixture liquid obtained by mixing hydrogen fluoride water solution and ethanol at 1:1 is employed as an electrolyte employed for anodic oxidation. In the oxidizing step, a lamp annealing device is employed. After a substrate temperature has been increased for a short time from room temperature to 900xc2x0 C. in dry oxygen, the substrate is maintained at 900xc2x0 C. for one hour, and the substrate is oxidized. Then, the substrate temperature is lowered to room temperature.
As shown in FIG. 27, the thus formed drift layer 6xe2x80x2 is considered as being composed of: at least a columnar polycrystalline silicon grain 51; a thin silicon oxide film 52 formed on a surface of the grain 51; a silicon nanocrystal 63 with its nanometer order interposed across the grains 51; and a silicon oxide film 64 formed on a surface of the silicon nanocrystal 63 and having its smaller film thickness than the crystalline particle size of the silicon nanocrystal 63. That is, in the drift layer 6xe2x80x2, the surface of each grain 51 contained in the polycrystalline layer before carrying out anodic oxidation processing is made porous, and a crystalline state is maintained at the center portion of each grain 51.
Therefore, a majority of the electric field applied to the drift layer 6xe2x80x2 is intensively applied to the silicon oxide film 64. As a result, the injected electrons are accelerated by a strong electric field relevant to the silicon oxide film 64, and drift among the grains 51 in an orientation indicated by the arrow A toward the surface. Thus, electron emission efficiency can be improved. Here, the electron source 10xe2x80x2 utilizes a ballistic conducting phenomenon that occurs by setting the size (crystalline particle size) of the silicon nanocrystal 63 and the film thickness of the silicon oxide film 64 equal to or smaller than the film thickness (a degree of electron mean free path) when an electron tunneling phenomenon occurs. Electrons arrived at the surface of the drift layer 6xe2x80x2 are considered as hot electrons. These electrons easily tunnels the surface electrode 7, and are emitted into a vacuum. In the electron source 10xe2x80x2 comprising the drift layer 6xe2x80x2, a heat generated in the drift layer 6xe2x80x2 during electron emission is radiated through the grain 51. Thus, the heat generated in the drift layer 6xe2x80x2 can be efficiently radiated, and an occurrence of a hopping phenomenon can be restricted.
As shown in FIG. 28, there is proposed an electron source 10 having an electrically conductive layer 12 formed on one surface of an insulating substrate 11 consisting of a glass substrate without employing an n-type silicon substrate as an electrically conductive substrate. In FIG. 28, like a constituent element similar to the electron source 10xe2x80x2 shown in FIG. 26 is designated by a line reference numeral. A description thereof is omitted here. The drift layer 6xe2x80x2 of the electron source 10xe2x80x2 shown in FIG. 28 is formed in accordance with a process similar to a case of the electron source 10xe2x80x2 shown in FIG. 26.
Procedures for emitting electrons from the electron source 10xe2x80x2 shown in FIG. 28 are basically similar to those in the case of the electron source 10xe2x80x2 shown in FIG. 26. However, the procedures are different from each other in that the direct current voltage Vps is applied between the surface electrode 7 and the electrically conductive layer 12 so that the surface electrode 7 becomes high in potential (positive polarity) relevant to the electrically conductive layer 12. In this manner, even in the electron source 10xe2x80x2 shown in FIG. 28, electrons can be emitted in the same way as the electron source 10xe2x80x2 shown in FIG. 26.
In recent years, as a device comprising a porous semiconductor layer that contains a semiconductor nanocrystal with a number of nano-orders formed by oxidizing the semiconductor layer at an anode, there is proposed a memory element (memory device) utilizing a new principle of operation which occurs in a nano-region (for example, Japanese Patent Laid-Open Publication No. 2001-222892). This memory element includes a storage layer for storing information by closing a carrier in a semiconductor nanocrystal with its nano-order capable of dosing a carrier, the carrier being covered with an insulating film.
However, in the above described conventional electron sources 10xe2x80x2, although electrons can be emitted constantly with high electron emission efficiency, the dielectric strength is comparatively low, and the service life is comparatively short. Therefore, improvement of the dielectric strength and longer service life are expected.
In the step of forming the drift layer 6xe2x80x2 of the above described conventional electron source 10xe2x80x2, the oxidizing step is carried out after the anodic oxidation processing step. If a water component or a fluorine component remains in the porous polycrystalline silicon layer formed in the anodic oxidation processing step, these residual components affect silicon oxide films 52 and 64. Thus, there is a danger that the electron source 10xe2x80x2 fails due to insulation destruction or the service life is reduced. That is, the silicon oxide films 52 and 64 are thermal oxide film formed in accordance with a rapid heating technique. Thus, if the water component or fluorine component remains, the residual components such as water component or fluorine component react with each other or are mixed when the silicon oxide films 52 and 64 are formed. In this manner, the film thickness of the silicon oxide films 52 and 64 becomes non-uniform or the film quality is degraded. As a result, there is a problem that a dielectric strength failure occurs, and the yield is lowered.
In addition, in a process for manufacturing the above described electron source 10xe2x80x2, anodic oxidation processing is a wet process, and thus, the thickness of a porous region or the size of silicon nanocrystal and its distribution becomes non-uniform in plane. As a result, the size or distribution of the silicon nanocrystal 63 in the drift layer 6xe2x80x2 becomes non-uniform. Thus, an in-plane distribution occurs with electron emission characteristics (such as current density of emission current or electron emission efficiency), and a defect locally occurs. There is a problem that an insulation destruction occurs, and the service life is reduced. In addition, there is another problem that it is difficult to obtain uniformity of the in-plane distribution, and thus, it is difficult to produce a large area.
In the meantime, in the step of forming the drift layer 6xe2x80x2 of the above described electron sources 10, the porous polycrystalline silicon layer after the anodic oxidation processing step is active. Thus, if a film is exposed to the air between the anodic oxidation processing step and the oxidizing step (for example, a stay period of unfinished items), a natural oxide film is formed on the surface of the silicon nanocrystal and polycrystalline silicon each configuring a porous polycrystalline silicon layer. As a result, there is a danger that such natural oxide film affects the dielectric strength of the silicon oxide films 52 and 64, the electron source 10xe2x80x2 fails due to insulation destruction, or the service life is reduced. That is, the silicon oxide films 52 and 64 are thin oxide films with their nanometer order, and thus, a rate of film thickness of a natural oxide film occupied in the entire film thickness of the silicon oxide films 52 and 64 increases. Thus, the silicon oxide films 52 and 64 with their high defect density are formed due to the presence of the natural oxide film, and it has become difficult to control the film thickness of the silicon oxide films 52 and 64. As a result, there occurs a problem that a dielectric strength voltage failure or the like occurs, and the yield is lowered.
As shown in FIG. 29, in the electron source 10xe2x80x2 having the drift layer 6xe2x80x2 formed by utilizing anodic oxidation processing, the size (crystalline particle size) of the silicon nanocrystal 63 that is a semiconductor nanocrystal in the drift layer 6xe2x80x2 deviates. Thus, the silicon nanocrystals 63 covered with the silicon oxide film 64 whose surface is an insulating film deviate from each other, and are formed discontinuously. Then, a distribution of the silicon nanocrystals 63 becomes non-uniform. As a result, there is a problem that the scattering probability of electrons increases, and the electron emission efficiency is lowered. Further, there is a problem that degradation with an elapse of time occurs due to an increase in electron scattering, and the service life of the electron source 10xe2x80x2 is reduced.
In a memory element having a storage layer formed by utilizing anodic oxidation processing, when the sizes of semiconductor nanocrystals deviate from each other, and are formed discontinuously, and a distribution of the semiconductor nanocrystals becomes non-uniform, there occurs a problem that it is difficult to control a write location of information in the storage layer, and the storage capacity is reduced.
As has been described previously, in the drift layer 6xe2x80x2 in the above described conventional electron source 10xe2x80x2, the porous polycrystalline silicon layer is oxidized, whereby a thin silicon oxide film is formed on a surface of a respective one of a number of silicon nanocrystals and a number of grains contained in the porous polycrystalline silicon layer. Then, for the purpose of forming a silicon oxide film with its good film quantity on all the silicon nanocrystals and grains, when the drift layer 6xe2x80x2 is formed, the porous polycrystalline silicon layer is electrochemically oxidized in an electrolytic solution consisting of a water solution such as 1 mol/1 of sulfuric acid or nitric acid. The electrolytic solution contains 90% or more (90 wt %) of water at a mass rate. The porous polycrystalline silicon layer is electrochemically oxidized, whereby the process temperature can be reduced compared with a case of rapidly heating the porous polycrystalline silicon layer, thereby forming the drift layer 6xe2x80x2, and thus, a restriction on a substrate material is reduced. Therefore, a large area for the electron source 10xe2x80x2 and cost reduction can be achieved.
However, in the electron source in which the porous polycrystalline silicon layer is electrochemically oxidized in the electrolytic solution consisting of a water solution such as sulfuric acid or nitric acid, thereby forming the drift layer, there is a problem that the emission current Ie or electron emission efficiency is small (insufficient) on an aspect of industrial utilization. In addition, there is a problem that the diode current Ips gradually increases, and the emission current Ie gradually decreases. Such problems is considered to occur the fact, when the drift layer 6xe2x80x2 is formed, the oxidization of the porous polycrystalline silicon layer is carried out in the electrolytic solution consisting of a water solution such as sulfuric acid or nitric acid. That is, 90 wt % or more of water is contained in the electrolytic solution. Thus, a large amount of bonding associated with water molecules such as Sixe2x80x94H, Sixe2x80x94H2, or Sixe2x80x94OH exists in the silicon oxide film formed in the drift layer 6xe2x80x2. Therefore, it is considered that the fineness of the silicon oxide film is impaired, the scattering of electrons easily occurs, and the dielectric strength is lowered.
The present invention has been made in order to solve the foregoing problem. It is an object of the present invention to provide a method of, and apparatus for, manufacturing an electron source in which a dielectric strength is easily improved, a service life is easily extended, and a large area is easily achieved.
It is another object of the present invention to provide a method of, and apparatus for, manufacturing an electron source capable of controlling the size or distribution of a semiconductor nanocrystal.
It is a further object of the present invention to provide a method of, and apparatus for, manufacturing an electron source with its high electron emission characteristics and high safety with an elapse of time.
An electron source (field emission type electron source) manufactured in accordance with a method according to the present invention includes: an electrically conductive substrate, a drift layer (strong field drift layer) formed on one surface of the electrically conductive substrate; and an electrically conductive thin film formed on the drift layer. In this electron source, a voltage is applied so that the electrically conductive thin film becomes positive in polarity relevant to the electrically conductive substrate. In this manner, electrons injected from the electrically conductive substrate into the drift layer drift the inside of the drift layer, and are emitted through the electrically conductive thin film. The method of manufacturing this electron source includes: an anodic oxidation processing step of, when a drift layer is formed, forming a porous semiconductor layer that contains a semiconductor nanocrystal in accordance with anodic oxidation; and an insulating film forming step of forming an insulating film on the surface of each semiconductor nanocrystal. In the anodic oxidation processing step, anodic oxidation processing is carried out while emitting light that essentially contains a wavelength of a visible light region relevant to the semiconductor layer. According to the method of manufacturing this electron source, the size or distribution of the semiconductor nanocrystal contained in the porous semiconductor layer can be controlled. In this manner, porous semiconductor layer in which a number of semiconductor nanocrystals are continuously distributed can be formed.
In the method of manufacturing this electron source, it is preferable that the wavelength of light emitted to the semiconductor layer be restricted by an optical filter. In this case, the wavelength of light emitted to the semiconductor layer can be easily adjusted.
Here, it is preferable that the optical filter be composed of at least one of an infrared cutting filter and a ultra-violet cutting filter. By doing so, a temperature rise caused by infrared rays that do not contribute to a porous film can be restricted. In addition, an amount of hole generation increases due to the ultra-violet rays, and the occurrence of a deviation in size or distribution of semiconductor nanocrystals can be restricted. Thus, the size or distribution of semiconductor nanocrystals contained in the porous semiconductor layer can be easily controlled.
In the method of manufacturing the electron source according to the present invention, it is preferable to set the wavelength of light to be emitted in the semiconductor layer at a wavelength at which the semiconductor nanocrystals are continuously connected to each other. In this case, a porous semiconductor layer in which a number of semiconductor nanocrystals with nanometer order are continuously connected to each other can be formed without employing an optical part such as an optical filter.
In the method of manufacturing the electron source according to the present invention, it is preferable to employ a light source of a monochromatic light. In this case, a porous semiconductor layer in which semiconductor nanocrystals of the same size are continuously connected to each other can be safely formed.
In the method of manufacturing the electron source according to the present invention, it is preferable to change the wavelength of light to be emitted in the semiconductor layer based on an elapse of time after anodic oxidation has started. In this case, the sizes of semiconductor nanocrystals can be controlled relevant to the thickness direction of the porous semiconductor layer. Namely, the sizes of the semiconductor nanocrystals can be differentiated relevant to the thickness direction of the porous semiconductor layer.
In the method of manufacturing the electron source according to the present invention, it is preferable to change the transmission wavelength of the optical filter based on an elapse of time after anodic oxidation has started. In this case, the sizes of the semiconductor nanocrystals can be controlled relevant to the thickness direction of the porous semiconductor layer.
Namely, the sizes of the semiconductor nanocrystals can be differentiated relevant to the thickness direction of the porous semiconductor layer.
In the method of manufacturing the electron source according to the present invention, it is preferable to intermittently emit light in the semiconductor layer. In this case, a temperature rise of the semiconductor layer can be restricted. In this manner, the size or distribution of the semiconductor nanocrystals in the porous semiconductor layer can be easily controlled.
In the method of manufacturing the electron source according to the present invention, it is preferable to emit light to the semiconductor layer from an opposite side to the surface of the semiconductor layer. In this case, a hole can be efficiently supplied from the opposite side to the surface as well as the surface side of the semiconductor layer. Here, the wavelength of both lights emitted from both sides in the thickness direction of the semiconductor layer may be changed synchronously. By doing this, holes can be supplied at both sides in the thickness direction of the semiconductor layer. Thus, even in the case where the thickness of the semiconductor layer is comparatively thick, this processing can be easily carried out. When the semiconductor layer is more porous, a band gap increases. Thus, larger energy is required to ensure that the layer is more porous. In general, when the wavelength is reduced, the light invasion depth becomes shallow. However, the semiconductor layer can be easily made more porous by thus emitting light from both sides in the thickness direction of the semiconductor layer. In addition, the sizes of the semiconductor nanocrystals formed in the porous semiconductor layer can be uniformed in the thickness direction of the porous semiconductor layer.
In the method of manufacturing the electron source according to the present invention, it is preferable to employ control means for controlling the concentration of an electrolyte in an anodic oxidation processing vessel so that forming of the porous semiconductor layer advances at the same velocity. In this case, in forming the porous semiconductor layer, the concentration of the electrolyte is controlled so that the velocities of producing a more porous semiconductor layer are identical to each other in a plane of a conductor layer. Thus, a process for anodic oxidation is stabilized, and the uniformity and reproducibility of the size or distribution of semiconductor nanocrystals contained in the porous semiconductor layer can be improved. As a result, the uniformity and reproducibility of size and distribution of the semiconductor nanocrystals in the drift layer can be improved. Therefore, the dielectric strength can be improved, and the service life can be extended. In addition, there can be provided an electron source with its high uniformity in a plane with electron emission characteristics and with a large area.
Here, it is preferable to utilize a control vessel for introducing an electrolyte with its adjusted temperature and concentration into an anodic oxidation processing vessel. In this case, the controllability of velocity for producing a more porous layer is improved. In this manner, the uniformity and reproducibility in a plane of the porous semiconductor layer can be improved. In addition, it is preferable that control means be provided to finely move a target comprising a lower electrode and a semiconductor layer. In this case, the uniformity and reproducibility of size and distribution of semiconductor nanocrystals contained in the porous semiconductor layer can be improved more remarkably.
In the method of manufacturing the electron source according to the present invention, it is preferable that the rinse step of removing the electrolyte remaining in the porous semiconductor layer by employing at least a hydrophilic organic solvent be included between the anodic oxidation processing step and insulating film forming step. In this case, the electrolyte or the like remaining in the porous semiconductor layer formed in accordance with the anodic oxidation processing step can be removed before the insulating film forming step. Thus, the quality of an insulating film formed on the surface of the semiconductor nanocrystals in the insulating film forming step can be improved. Therefore, the dielectric strength of the electron source can be improved, and the service life can be extended.
In the method of manufacturing the electron source according to the present invention, it is preferable that the rinse step of removing the electrolyte remaining in the porous semiconductor layer by employing at least a non-soluble organic solvent be included between the anodic oxidation processing step and the insulating film forming step. In this case, the electrolyte or the like remaining in the porous semiconductor layer formed in accordance with the anodic oxidation processing step can be removed before the insulating film forming step. Thus, the quality of an insulating fair formed on the surface of the semiconductor nanocrystal in accordance with the insulating film forming step can be improved. Therefore, the dielectric strength of the electron source can be improved, and the service life can be extended.
In the method of manufacturing the electron source according to the present invention, during a period specified between the anodic oxidation processing step and the oxidization processing step, it is preferable to prevent a natural oxide film from being formed on the surface of the semiconductor nanocrystal without exposing the porous semiconductor layer to the air. In this case, during the above specified period, the natural oxide film can be prevented from being formed on the surface of the semiconductor nanocrystal. Thus, the quality of the oxide film formed on the surface of the semiconductor nanocrystal in accordance with the oxidization processing step can be improve. Therefore, the dielectric strength of the electron source can be improved, and the service life can be extended.
During the above specified period, it is preferable to cover the surface of the porous semiconductor layer with a non-oxide liquid. By doing this, in the case where such a non-oxide liquid is employed for rinsing in accordance with the anodic oxidation processing step, for example, the natural oxide film can be prevented from being formed by utilizing such a non-oxide liquid. In addition, in the above specified period, atmosphere may be used as an inert gas. By doing this, contamination of the porous semiconductor layer can be restricted. In the above specified period, at least the porous semiconductor layer may be held in a vacuum. By doing this, the adhering of impurities to the porous semiconductor layer can be restricted.
In the method of manufacturing the electron source according to the present invention, it is preferable that the insulation film forming step includes the main oxidization processing step of electrochemically oxidizing the porous semiconductor layer in an electrolyte having a solute dissolved in an organic solvent. In this case, an emission current or electron emission efficiency and the like increases as compared with the prior art, and the stability of electron emission characteristics of the electron source with an elapse of time can be improved. One of the reasons what the emission current and electron emission efficiency are thus improved, and the stability of electron emission characteristics with an elapse of time is improved is stated as follows. That is, this is because the density of the oxide film increases, and the dielectric strength of the oxide film is improved as compared with a conventional technique for electrochemically oxidizing the porous, polycrystalline silicon layer in an electrolytic solution consisting of a water solution such as sulfuric acid or nitric acid, thereby forming a drift layer. In addition, as compared with a case in which the porous semiconductor layer is thermally oxidized rapidly, thereby forming a drift layer, a process temperature can be reduced, an area for an electron source can be increased, and cost reduction can be achieved.
In the method of manufacturing the electron source that contains the main oxidization processing step, it is preferable to add water to an electrolytic solution. By doing this, in the case where there is employed a substance having its small solubility to an organic solvent serving as a solute and having its large solubility to water, the concentration of the solute in the electrolytic solution can be increased by adding water. Thus, the film quality of the oxide film is improved. In addition, as the concentration of the solute increases, the conductivity of the electrolytic solution increases. Therefore, a deviation in plane of the film thickness of the oxide film can be restricted.
In the method of manufacturing the electron source including the main oxidization processing step, it is preferable that the auxiliary oxidization processing step of oxidizing the porous semiconductor layer in accordance with a thermal oxidization technique be included at least before or after the main oxidization processing step. By doing this, the density of the oxide film can be improved more remarkably.
In the method of manufacturing the electron source that contains the main oxidization processing step, the pre-oxidization processing step of oxidizing the porous semiconductor layer before the main oxidization processing step may be included. In this case, the density of the oxide film can be improved more remarkably. Further, in the thickness direction of the drift layer, the film thickness of the oxide film existing in a region that is comparatively close to the electrically conductive thin film can be restricted from being larger than that of the oxide film that exists in a region that is comparatively distant from the electrically conductive thin film. In this manner, electron emission efficiency and stability with an elapse of time can be improved. In addition, the pre-oxidization processing step of oxidizing the porous semiconductor layer before the main oxidization processing step and auxiliary oxidization processing step may be included. In this case as well, in the thickness direction of the drift layer, the film thickness of the oxide film existing in a region that is comparatively close to the electrically conductive thin film can be restricted from being larger than that of the oxide film existing in a region that is comparatively distant from the electrically conductive thin film, and in this manner, electron emission efficiency and stability with an elapse of time can be improved.
In the method of manufacturing the electron source that contains the main oxidization processing step, the rinse step of rinsing the porous semiconductor layer may be included after the main oxidization processing step. In this case, even if impurities such as alkali metal or heavy metal enter the porous semiconductor layer, such impurities can be removed in the rinse step. As a result, the electron emission characteristics of the electron source can be stabilized and long-term reliability can be improved.
In addition, an apparatus for manufacturing the above electron source according to the present invention includes: an anodic oxidation processing device for, when a drift layer is formed, forming a porous semiconductor layer that contains a semiconductor nanocrystal in accordance with anodic oxidation; and an insulating film forming device for forming an insulating film on the surface of each semiconductor nanocrystal. Here, the anodic oxidation processing device is designed to carry out anodic oxidation processing while emitting light that essentially contains the wavelength in a visible light region relevant to the semiconductor layer. According to this electron source manufacturing apparatus, the size or distribution of semiconductor nanocrystals contained in the porous semiconductor layer can be controlled. In this manner, there can be formed a porous semiconductor layer in which a number of semiconductor nanocrystals are distributed to be continuously connected to each other.